Unit 3 – Light and Optical Systems Some of the stuff we’ve covered so far (whether you realize it or not…)

Sources of Light Just the powerpoint you copied earlier Terms to know: light, natural light source, radiates, radiant energy, artificial light source, incandescent, fluorescent, phosporescent, chemoluminescent, bioluminescent, luminous, non-luminous.

The Ray Model of Light A ray is a straight line that represent the path of a beam of light Example: Light from this projector cannot bend around me if I stand in front of it – thus a shadow is created Therefore, light must travel in straight lines

Ray Model (cont.) The ray model helps us to understand what happens to light when it reaches certain materials When light passes through a material and continues on in a straight line, the material is said to be transparent Materials that let some light through, but bend the light rays are said to be translucent Materials that block all light from passing are called opaque – they cast shadows

Reflection Reflection is the process in which light strikes a surface and bounces back off that surface Did you realize that as you read these words on the screen you are seeing reflected light? The difference between a mirror and the screen is determined by the surface that is doing the reflecting

Reflection (cont.) The ray that comes from a light source is called the incident ray The light that is reflected off a mirror or the screen is called the reflected ray As in your light sketches, the line you drew perpendicular to your reflective surface is called the normal line

Reflection (cont.) The angle between the normal line and the incident ray is called the angle of incidence The angle between the normal line and the reflected ray is called the angle of reflection The first few experiments used a plane mirror to show this (flat surface)

The Law of Reflection If you did your drawings accurately, you would have noticed that there was a relationship between the angle of incidence and the angle of reflection The Law of Reflection states “the angle of reflection equals the angle of incidence”

Law of Reflection (cont.) If this Law did not exist, you would stand in front of a mirror and your reflection might be somewhere else instead of in front of you. If this Law did not exist you would try and read a book but the light reflecting off the book might not bounce back properly to hit your eye and allow you to see the pages!!!